Process for purifying tetrahydrofurans used as starting material for polyether polyols

Abstract

Tetrahydrofurans suitable for use as starting materials in the synthesis of polyether polyols without causing coloration in the product polyether polyols can be obtained by contacting crude tetrahydrofurans with a mineral acid or a strongly acidic cation-exchange resin, followed by isolation through a simple distillation and/or rectification to obtain purified tetrahydrofurans.

What is claimed is:  
     
       1. A method for purifying a crude tetrahydrofuran which is then suitable for the preparation of a polyether polyol comprising: 
       contacting said crude tetrahydrofuran represented by the general formula (1) with mineral acid selected from the group consisting of nitric acid, sulfuric acid and phosphoric acid, said contacting being conducted at a temperature from the room temperature up to the boiling point of said tetrahydrofuran, and  
       then instantly distillating by at least one of a simple distillation or a rectification, wherein said general formula (1) is:                    
       wherein R 1  and R 2  represent a hydrogen atom or an alkyl group of normal chain or graft whose carbon number is 1 to 5 and can be same or not be same.  
     
     
       2. The method for purifying a tetrahydrofuran according to claim  1 , wherein said method comprises contacting said crude tetrahydrofurans with mineral acid, and then instantly distillating by at least one of a simple distillation or a rectification. 
     
     
       3. The method for purifying a tetrahydrofuran according to claim  1 , wherein said method comprises contacting said crude tetrahydrofurans with mineral acid, to obtain an acidified solution, neutralizing the solution by adding an alkaline aqueous solution containing alkali metal or alkaline-earth metal in an amount which is more than an equivalent volume to the added volume of said mineral acid, and then instantly distillating by at least one of a simple distillation or a rectification. 
     
     
       4. The method for purifying a tetrahydrofuran according to anyone of claims  1 ,  2 , and  3 , wherein the volume of said mineral acid to be added is 0.1 to 15% by weight relative to the crude tetrahydrofurans. 
     
     
       5. The method for purifying a crude tetrahydrofuran which is then suitable for the preparation of a polyether polyol comprising contacting said crude tetrahydrofuran represented by the general formula (1):                    
       wherein R 1  and R 2  independently represent a hydrogen atom or a straight or branched alkyl group having 1-5 carbon atoms, with a high acid cationic ion exchange resin,  
       wherein said high acid cationic ion exchange resin is a sulfonic acid type cationic ion exchange resin, and the quantity of said ion exchange resin to be added is 1 to 30% by weight relative to the crude tetrahydrofuran, and  
       then conducting a least one of simple distillation or rectification and then recovering the purified tetrahydrofuran.  
     
     
       6. The method for purifying a tetrahydrofuran according to claim  1  or  2 , wherein contacting the crude tetrahydrofuran with said mineral acid and the purifying of the crude tetrahydrofuran by said mineral acid and the distilling as a single distillation are carried out at the same time. 
     
     
       7. The method for purifying a tetrahydrofuran according to claim  3 , wherein said alkaline aqueous solution is an aqueous sodium hydroxide or potassium hydroxide solution. 
     
     
       8. The method for purifying a tetrahydrofuran according to claim  1 , wherein said method for purifying tetrahydrofurans is carried out in series. 
     
     
       9. The method for purifying a tetrahydrofuran according to claim  1 ,  2  or  5 , wherein said tetrahydrofuran represented by said general formula (1) is 3-alkyl tetrahydrofuran. 
     
     
       10. The method for purifying a tetrahydrofuran according to claim  9 , wherein said tetrahydrofuran represented by said general formula (1) is 3-methyl tetrahydrofuran. 
     
     
       11. The method for purifying a tetrahydrofuran according to claim  9 , wherein said tetrahydrofuran represented by said general formula (1) is 3-ethyl tetrahydrofuran.